Industrial waste water is one of the most serious environmental pollutants. It is therefore absolutely necessary to properly treat it, getting rid of toxic substances therein and then separating water from mud, the water to be drained into a river or the like. The dehydrated mud block must then be properly discarded or disposed of.
A mud dehydrating system is used to separate water from mud in treated industrial dense waste water, and a conventional one is shown in FIG. 7. The conventional dehydrator includes a mud treating tank 11, a centrifugal dehydrating cylinder 12, an endless circulating upper and a lower filter cloth 13, 14, a compressing roller unit 15 and a filter cloth cleaning and washing unit 16 as main components.
The mud treating tank 11 receives waste water mixed with mud from a condensing pool and into which a chemical is added to mix evenly with the waste water with mud. Then the treated waste water with mud is moved into the centrifugal dehydrating cylinder 12, wherein free water in an upper layer of the waste water is removed, and a jelly-like mud sinks to the bottom and then drops down onto the upper filter cloths 13 moving on the first stage grid gravitational dehydrating section 17 so that water dripping down from the upper filter cloths 13 falls down through the grip section 17 and is collected for recycling. After that, the mud mass on the upper filter cloths 13 is gradually moved and falls down on the lower filter cloth 14 moving on a second grid gravitational dehydrating section 18 to be dehydrated gravitationally for the second time. Then the mud mass on the lower filter cloth 14 gradually moves to be pinched between the upper and the lower filter cloths 13, 14 and to be compressed and squeezed by a plurality of compressing rollers of a compressing roller unit 15, releasing water contained therein. And finally, the mud mass becomes a mud block of a certain thickness with little moisture, and is removed at two transmitting rollers 151, 152 by two knives, one upper 153 and one lower 154. The mud blocks fall down to a collection section to be transported for discarding. Meanwhile, the water freed from the waste is collected in an upper and a lower plate 171, 181 and then recycled to be used for the cleaning and washing unit 16 or drained into a river.
The cleaning and washing unit 16 shown in FIGS. 8 and 9 includes a projecting cover 161 on the table 10, a water inlet tube 162 inside the cover 161, and a plurality of nozzles 163 connected under the tube 162, each nozzle 163 having a straight slot mouth for spraying out a fan-shaped water curtain to wash the slow-moving upper and lower filter cloth 13, 14 to clean any mud dregs stuck on the cloths. Then the endless filter cloths 13, 14 can be repeatedly used for conveying the mud mass to be compressed and squeezed by the compression roller unit 15.
More than 12 nozzles 163 have to be provided in the cleaning and washing unit 16 to spray the fan-shaped water curtain, with each one fixed at 15 mm intervals. The washing unit consumes about 32 tons of water for 8 hours' operation of this unit, resulting in a heavy cost for a user.
The plurality of compressing rollers and the upper and the lower filter cloths 13, 14 play an important role in dehydrating a large part of water from the mud, which can become mud blocks containing little moisture. How the mud mass comes out of the second gravitational dehydrating section 18, enters the compressing roller unit 15, the entering quantity of mud, and the spreading of the mud mass is especially important. These characteristics are related to the shape of the front two rollers 157, 158 of the compressing roller unit 15 and the moving tension of the filter cloths 13, 14. The necessary tension of the cloths are given by the tension rollers 155, 156, so the shape of the rollers 155, 156 is comparatively important. As shown in FIG. 10, when a large mud mass begins to enter the space between the upper and the lower filter cloth 13, 14, it is pushed by the first roller to become gradually wide and flat; if the mud mass is too large, it can partly leak out from both sides of the cloths 13, 14. The two cloths 13, 14 have to be adjusted in tension by moving the tension rollers 155, 156 so as to squeeze out water from the mud mass.
How the tension rollers 155, 156 are to be moved is to be described as follows. As shown in FIGS. 11, 12, a long oval hole 101 is respectively provided in both side portions of the table 10, two angle irons 103, 103 with guide rails 102, 102 are fixed at both sides of each hole 101, a movable bearing 104 is provided between the two rails 102, 102, and a rack 105 is provided in the inside of the table 10. The tension roller 155 has a shaft 1551 pivotally combined with the bearing 104, a gear 1553 is provided to engage the rack 105, and one end of the movable bearing 104 is fixed to an end of a shaft 191 of a pressure augmenting unit 19 so that the two ends of the shaft of the tension roller 155 can be moved by the pressure augmenting unit 19 to pull the filter cloth 13 or 14 to a proper tension.
Here we are going to make an inquiry into the relationship between the pressure augmenting unit 19 and the filter cloths 13, 14. As mentioned above, the tension rollers 155, 156 are displaced to pull the upper and the lower filter cloths 13, 14 to a proper tension to force the mud mass to dehydrate. The pressure augmenting unit 19 may include an oil or air cylinder. However, an oil cylinder is generally expensive, and has a high failure rate, and liable to get dirty in its work location. In addition, oil cylinders have a large output because of the incompressibility of the oil as mobile medium, which is hard to adjust to provide a small force. Such circumstances result in shorter service life for the filter cloths 13, 14.
If an air cylinder is used for the pressure augmenting unit 19, its output is adjustable. However, air as mobile medium has a characteristic of compressibility. Using air, the filter cloths 13, 14 may gradually grow slack after long hours of operation because of the weight and dimensions of the mud mass. This will result in the mud mass blocks produced gradually containing more and more moisture. Also, the upper and the lower filter cloths 13, 14 may move too near to and rub both inner sides of the table 10, and then become damaged or suddenly break, if their tension is not proper.